1. Field of the Invention
The invention relates to wayside signaling generally and more particularly to wayside signal acknowledgment systems.
2. Discussion of the Background
Trains are often controlled by wayside signaling systems. A wide variety of wayside signal systems are known in the art. In traditional wayside signaling systems (e.g., Automated Block signaling (ABS) and Centralized Track Control (CTC) systems), one or more colored signal lights mounted on poles alongside a track are used to direct a train operator as to how to move the train. These wayside signals may be located at various positions on the railway such as near the beginning of a block of track and near grade crossings, sidings, switches, etc.
The signal lights indicate whether and under what conditions (e.g., what speed) a train is to proceed in a section of track associated with the signal. The meaning of the wayside signal is sometimes referred to as the signal “aspect.” As one simple example, a red signal indicates that a train cannot enter a section of track associated with a signal, a yellow signal indicates that the train can proceed through a section of track at a speed that will allow it to stop before entering the next section of track, and a green signal indicates that the train may proceed through a section of track at the maximum allowable speed. Other more complex signaling systems are also known in the art. On some railroads, there are over 125 different colored light signal indications that must be recognized and obeyed.
An operator is required to observe the lights and operate the train accordingly. However, train operators are human and can sometimes miss a signal, which can result in disaster. A number of systems have been designed to address this problem, but each of these systems has drawbacks that make them unsuitable for some applications.
Several of these systems, sometimes referred to as communication-based train control (CBTC) systems, involve the communication of a signal information into the cab of a train. For example, in a prior art system referred to as the Cab Signal system, wayside signals are transmitted as alternating current signals from wayside signal equipment through the rails of the train track, where they are picked up by inductive coils mounted on the locomotive and displayed to the operator on a display located in the locomotive cab. The Cab Signal system forces the operator to acknowledge signals that are more restrictive than the current signal and, in some systems, will activate the train's brakes to stop the train if a signal is not obeyed. However, this system has several drawbacks. First, it requires the installation of expensive wayside equipment to transmit the signal to the locomotive cab through the rails.
Second, the system only requires acknowledgment of signals. Simply requiring acknowledgment of signals does not ensure that an operator is alert. It is known to those of skill in the art that operators can successfully acknowledge signals while in only a semi-conscious state referred to as “micro-sleep.” Although some embodiments of the cab signal system will stop the train if a signal is not obeyed, this after-the-fact response may not be sufficient to prevent an accident. Furthermore, neither a semi-conscious crew member nor the cab signal system may respond to events such as a person or other obstruction on a train track for which the wayside signaling system does not provide a warning, whereas a fully alert crew member could take appropriate action in such an event.
Third, the cab signal system does not force an operator to acknowledge less restrictive signals. This is disadvantageous because if an operator misses a less restrictive signal, the operator may miss an opportunity to operate the train more efficiently by increasing the speed of the train.
Other systems involve the transmission of wayside signals to the cab of the train using radio-based communications. In these systems, signal information is broadcast to the cab of the train using radio frequency transmissions. Although the radio frequency communication equipment used in such systems is less expensive than the equipment used in the cab signal systems, it still increases costs, especially in a railroad in which a wayside signaling system is already in place.
There is a system described in U.S. Pat. No. 6,112,142 (the contents of which are hereby incorporated by reference herein), which is owned by the assignee of the present invention, that does not require wayside communication equipment in addition to existing wayside signal equipment. In that system, an engineer and a trainman are each provided with a combined display/input device referred to therein as a pendant. When a train with such a system approaches a signal, both the engineer and the trainman must agree as to the signal aspect by pressing corresponding buttons on the pendant corresponding to the signal aspect. If both the engineer and the trainman agree as to the signal aspect, the system will automatically ensure compliance with the signal. If the engineer and the trainman do not agree as to the signal aspect, or do not operate the train in compliance with the signal, the system will take corrective action to enforce the signal and/or stop the train. Some embodiments of that system combine a global positioning system or inertial navigation system with a track database containing the locations of wayside signals to provide the train crew with a signal proximity warning and will stop the train if the train crew fails to acknowledge this warning. While this system is advantageous in that it does not require any equipment to transmit signals to trains in the system in addition to a wayside signaling system, it has the drawback of requiring two crew members.
What is needed is a system and method that overcomes these and other deficiencies in known systems.